Autoradiographic Studies of Beta-Adrenergic Receptors

Abstract

A great deal of information concerning the properties, functions, and regulation of beta-adrenergic receptors has come from studies utilizing either whole organs or homogenized or soluble preparations from organs (Wolfe et al., 1977; Lefkowitz et al., 1984; Wolfe and Molinoff, 1988). These types of experiments have led to our current understanding of how these receptors are functionally coupled to adenylate cyclase and how tissues respond to either increases or decreases in the level of receptor stimulation (often by changing the number or properties of the receptors). These types of studies, however, do not yield information regarding the localization of receptors, except on a relatively large anatomical scale where, commonly, entire tissues (e.g., cerebral cortex, heart, and so on) are used to study receptors. Additionally, studies utilizing radioligand binding to homogenized preparations of tissues require relatively large amounts of tissue. In response to these types of problems, the methodology of receptor localization using autoradiographic techniques has been developed. Autoradiography is a method, described in detail below, of localizing and quantifying neurotransmitter receptors in thin sections of tissues. Briefly, autoradiography involves the incubation of slide-mounted tissue sections with a radioligand that, hopefully, binds only to the receptor of interest, in this case beta-adrenergic receptors. Incubation is followed by exposure of the labeled sections to a film emulsion that is sensitive to the bound radioactivity. The exposed film emulsion is then processed, resulting in silver grains being developed where the radioligand was apposed. Correlations can be found that relate the density of silver grains in the film emulsion to the exact amount of radioactivity bound to a given amount of tissue sections with a radioligand that, hopefully, binds only to the receptor of interest, in this case beta-adrenergic receptors.